Process and device for eliminating the particles contained in a stream of fluid

ABSTRACT

The present invention relates to a process and a device for eliminating particles from a stream of fluid, having a channel for turbulent flow of the fluid and a series of objects placed along the channel.

[0001] The present invention relates to the elimination of fineparticles contained in gases. The present invention in particularfacilitates separation and recovery of particles such as dust, mist,vapors, smoke, and harmful gases, etc. dispersed in a gas having aturbulent flow regime, benefiting from certain effects linked toturbulence in a specific and novel manner and using purely mechanicalmeans.

[0002] Individuals skilled in the art of fluid mechanics and alliedfields know that the fine particles dispersed in a fluid havingturbulent flow tend to follow the vortices in the turbulent fluid.

[0003] Separation of very fine particles with sizes between 0.01 and 100microns and contained in industrial gases or in ambient air is a complexand expensive operation. The devices usually employed for this purposeinclude electrical dust removers, various filters, and wet dustremovers. Scrubbers are also used to eliminate the harmful gasescontained in industrial gases. Cyclone collectors are traditionallyemployed to eliminate particles greater than approximately 5 microns,and concerted efforts have recently been made to extend theireffectiveness to particles of approximately 1 micron.

[0004] The international patent application published under No. WO93/15,822 describes a method for eliminating fine particles dispersed ina stream of fluid using the mixing effect of turbulence to separate andrecover the fine particles in a specific and novel manner by passing thestream of fluid having turbulent flow through a channel with a freeinterior space along which is provided a zone communicating freely withthe flow channel, in which the flow is impeded by a large number ofobjects close to each other within the flow section, which convert theturbulent flow into a viscous flow. Turbulent eddies carrying particlespenetrate continuously into this zone, which forms a dilated viscousunderlying layer, and deposit the particles on the surfaces of theobjects present in this zone. Retention of the particles on the surfacesof the objects is improved if these objects are charged with staticelectricity. The devices operating according to the principle describedabove of recovery of the particles contained in fluid streams will becalled “turbulent flow dust removers.”

[0005] The present invention discloses means for effecting such aseparation of particles that are not described in document WO 93/15,822.In all the embodiments, the mechanism of dust recovery is the same,namely turbulent deposition by penetration of vortices. The presentpatent application applies to all the embodiments described here and tofuture modifications later made thereto and based on this principle.Certain dust recovery or elimination means are described here, but theydo not at all constitute the sole method for eliminating the dustcollected. Some are based on purely physical means (employing gravity)and others are based on mechanical means (such as a grating, screwconveyor, convertor belt, shaker mechanism, quick-return agitation,etc.) Certain embodiments are useful for small-scale applications (up to500 acfm), some are intended for medium-scale applications (up to 5000acfm), and others can be modified for application to large-scaleindustrial units, but all are based on the same basic principle: that ofturbulent deposition as described here and in Patent Application WO93/15,822 as well as in Patent Application GB 9407441.6 A large numberof the embodiments described can be used, in addition to elimination ofparticles, to eliminate harmful gases either by impregnation of thecollecting surface with a suitable catalyst or an adsorbent such asactivated charcoal, or by fine atomization of water or of a suitableaqueous solution injected into the turbulent gas with the collectingdevice. In the first case, the vortices continuously transport theharmful gas to the collecting surface where it reacts or is adsorbed. Inthe second case, the fine atomized jet is precipitated by turbulentdeposition after absorbing the harmful gas. In this case, the turbulentflow dust remover functions as a wet dust remover. Dry screening isanother area of application of the turbulent flow dust remover; it canbe used to recover dry particles formed during the process. Certainadditional means allowing recovery of particles are described below withreference to the attached figures wherein:

[0006]FIG. 1 is a front view of a plate disposed in a container and usedin first additional means;

[0007]FIG. 2 is a side elevation with exploded views: FIG. 2a of aturbulent flow dust remover according to second additional means; thequick-return mechanism FIG. 2b is a front view FIG. 2c of a screeningplate and a dust removal tray disposed in the container;

[0008]FIG. 3 is a side view of a turbulent flow dust remover accordingto one embodiment of third additional means;

[0009]FIG. 4 is a front view showing exploded views of a turbulent flowdust remover according to a second embodiment of the third additionalmeans;

[0010]FIG. 5a is a side view with exploded views (a) of a dust removeraccording to a third embodiment;

[0011]FIG. 5b is a cross section through a turbulent flow dust removeraccording to a third embodiment of the third additional means;

[0012]FIG. 6 is a perspective view with exploded views (a) and a crosssection perpendicular to the main axis (b) of a turbulent flow dustremover according to a fourth embodiment of the third additional means;

[0013]FIG. 7 shows two perspective views of a turbulent flow dustremover according to a fifth embodiment of the third additional means,of which one (7 a) shows exploded views and the other (7 b) shows thelocation of sections: a cross section along main axis FIG. 7c and twocross sections perpendicular to the main axis: FIG. 7d and FIG. 7e;

[0014]FIG. 8 shows a perspective view with exploded views FIG. 8a and ahorizontal section FIG. 8b of a turbulent flow dust remover according toa sixth embodiment of the third additional means; and

[0015]FIG. 9 shows a perspective view with exploded views of a turbulentflow dust remover according to a seventh embodiment of the thirdadditional means.

[0016] 1. First Additional Means, FIG. 1

[0017] In the first additional means shown in FIG. 1, it is possible toplace a relatively large number of plates 18 one behind the othertransversely in container 10, either by placing them on the bottom ofthe container, as described in document WO 93/15,822, or by leaving aspace between the bottom 20 of container 10 and the lower edges ofplates 18. The gas flows in channel 16 in the form of a turbulentstream. Some or all of the plates have a plurality of slots 8 alignedone behind the other, forming spaces, which can be designated by theterm “canyons,” and which pass through the set of plates 18. The widthof each of these slots or canyons is variable but is preferably betweenabout 3 mm and 10 mm. The spaces between the slots or canyons made inthe plates are also variable, but are preferably between approximately 1cm and approximately 30 cm. In tests performed on dispersed ASP 200 testdusts with a mean particle size of 1.8 μm, a container 10 that is 61 cmwide, a gas flow channel 16 that is 5 cm high, a plate spacing of 4 cm,a plate height of 15 cm, a gas flowrate of between 12 m/sec and 18m/sec, and a dust remover 3.4 m long, the recovery efficiency withplates that had no “canyons” was 48% while with plates that had 13“canyons” 3 mm wide the efficiency rose to 62%.

[0018] 2. Second Additional Means. FIG. 2

[0019] In the second means for effecting particle separation,illustrated in FIG. 2, instead of the plurality of closely settransverse plates described in document WO 93/15,822, a relatively largenumber of mesh screens 6, each supported by a frame 4, said screensbeing disposed one behind the other, and with a space of approximately0.5 cm to 2 cm between the bottom of dust removal tray 28 resting onsides 26 attached to the bottom of the channel, and the lower edge of ascreen. Pins 2 designed to strike the screens are attached to the sidesof tray 28. According to a preferred embodiment, a metal strip 18 with awidth of between approximately 1 cm and 4 cm can be placed on the upperedge of each screen, replacing said screen. The screens can be anyinterval apart, preferably between approximately 0.5 cm andapproximately 5 cm; they can be made of fibers, filaments, or metalwires with a diameter that is preferably between approximately 0.1 mmand approximately 1 mm. The size of the screen meshes can vary widelybut is preferably between approximately 1 mm and approximately 10 mm.This arrangement is similar to that described in document WO93/15,822.The dust-laden gas penetrates container 10 through inlet 12, and flowsthrough channel 16, and the cleaned gas is removed through outlet 14.The inlet and outlet have an edge 24. The fine particles are entrainedby vortices due to the gas that flows through the free passageway abovethe screens to the area occupied by the screens, where the vortices aredamped and the dust is deposited on the meshes of the screens (and onthe metal strips located on the upper edges of the screens) then, aftera deposit of sufficient thickness has formed, the deposited particlesfall into the bottom of the device. Dust removal tray 28 is attached toa heavy steel plate 52 that is shaken with an amplitude of approximately1 cm to 3 cm and at a frequency of approximately 2 Hz by means of shaft36, by a quick-return cam 38, by means of a bellows 34, or any othersuitable means, serving as a sealing element for drive shaft 36, and cam38 is driven by a motor 40. The forward-backward speed ratio isapproximately 2 or 3, the dust collected on the plate is sent to hopper46 while the dust continues to be collected without interruption. Thehopper is emptied by means of rotary valve 44. As can be seen in FIG. 2,the forward movement is from right to left. Another possibility is toplace hopper 46 at the opposite end of container 10 where the cleanedgas leaves the system through outlet 14 instead of being near inlet 12.However, the forward movement in this case will be from left to right.The use of the screen instead of plates is advantageous because itincreases the surface area accessible to the fine particles to becollected, which increases the particle recovery efficiency. The dustcollected at the bottom of the system by shaking by means of aquick-return mechanism can also be eliminated when plates are used,whether they have no “canyons” as described in document WO 93/15,822 orwhether they are provided with slots like those used in the first newmeans of the present invention.

[0020] 3. Third Additional Means, FIGS. 3, 4, 5, 6, 7, 8, and 9

[0021] In the third additional means designed for particle separation,instead of the plurality of close-set transverse plates or screens, amat made of a fibrous fabric or a pad disposed along the turbulent gasflow in the device is used. The fibrous fabric can be based onpolyester, glass, metal, or ceramic fibers and has a porosity (voidsratio) of preferably between approximately 0.90 and approximately 0.999;the diameters of its fibers are between approximately 0.001 mm andapproximately 0.1 mm so that there is an average space of approximately0.5 mm to 2 mm between two adjacent fibers. The fibers of the pad can becharged with static electricity and/or the pad can be pleated. Thethickness of the pad may be between approximately 1 cm and approximately30 cm. This new embodiment of the invention is similar to some extent tothe second additional means described in the present document, but itallows far finer collecting fibers to be used, so that the collectingsurface areas are greater than those available with the screens; inaddition, it offers certain advantages in construction and manufacture.The gas present in the high-porosity pads forms a dilated viscousboundary layer into which vortices from the turbulent gas streampenetrate and transport particles in suspension. The particles aretrapped by the fibers by any known recovery mechanism. While inconventional filters the gas is made to enter on one side of the filtermedium and to leave on the other side, bringing about an elevatedpressure loss and gradual clogging of the medium, in the presentinvention most of the gas flows along the porous pad in an open channel,ensuring a high rate of particle recovery at a stable rate, as well as adrop in pressure which remains at a constantly low level and a high gasflowrate.

[0022]3 a) In the embodiment of the third additional means presented inFIG. 3, the turbulent flow dust remover has a container 10, an inlet 12for the gas laden with fine particles, and an outlet 14 for the cleanedgas, disposed on a generally horizontal axis provided with edges 24.Inside container 10, the gas flows along passageway 16 below which is amat comprised of a fibrous pad 30 held by a cage of metal wires 32attached to a dust-removal tray 28 which is shaken intermittently orcontinuously by means of the quick-return mechanism described in thecontext of the embodiment illustrated by FIG. 2 and comprised of driveshaft 36, bellows 34, or another suitable sealing means, quick-returncam 38, and motor 40. During tests conducted with a pad of glass fibers10 cm to 15 cm thick and with a porosity of 99.5%, formed of fibers witha diameter of approximately 30 μm, these tests were conducted under thesame conditions as those described for the first additional means, therecovery efficiency was raised to 70%. This embodiment has otheradvantages such as the possibility of continuously eliminating the dustalready collected from the device, as well as the much lower cost andweight of the pad by comparison to the plates.

[0023]3 b) The embodiment presented in FIG. 4 has great similaritieswith the embodiment illustrated in FIG. 3. It has a similar container 10with an inlet 12 and an outlet 14 designed for the gas, and edges 24,but is disposed on an axis oriented about 70 degrees to the horizontal.The gas flows through channel 16, under which is a fibrous pad 30 heldby a cage of metal wires 32 welded to a heavy steel plate 52 which isshaken by a drive shaft 36 driven by a shaker mechanism 50 mounted on asupport 54 and operating at amplitudes and frequencies similar to thosedescribed relative to the embodiment of FIG. 2, but which is notnecessarily of the quick-return type. Bellows 34 or any other suitablemeans serves as a sealing element for drive shaft 36. The metal-wirecage slides on guides 26. The dust knocked off the fibers by the shakingfalls into dust removal channel 48 and slides on the bottom 20 ofcontainer 10 by gravity and falls into hopper 46 whence it is removedthrough rotary valve 44.

[0024]3 c) The third embodiment of the third additional means of theinvention is illustrated FIGS. 5a and 5 b. Container 10, inlet 12 andoutlet 14, edges 24, gas flow channel 16, dust removal plate 28 to whichis attached heavy steel plate 52, guides 26, bottom 20, the quick-returnmechanism including quick-return cam 38, drive shaft 36, the bellows orany other appropriate means 34, and motor 40, hopper 46, and rotaryvalve 44 are all identical to the corresponding components in theembodiment described with reference to FIG. 2 of this document. In thisembodiment, the fibrous fabric is used in the form of a belt moved atlow speed by shafts 56 equipped with pinions (not numbered). The dust iscollected by the belt in the upper run and is removed by dust removalshafts 76, also provided with pinions 104, in the lower run. The shaftsare controlled by a motor (not shown).

[0025] Dimensions The typical dimensions of all the embodimentsdescribed hereinabove are the following. The width of container 10 isbetween 10 cm and 1 m and preferably amounts to approximately 50 cm, theheight of flow channel 16 is between 1 cm and 20 cm and preferablyamounts to approximately 5 cm, the thickness of fibrous pad 30 isbetween 1 cm and 30 cm and preferably amounts to approximately 10 cm.The length of the container depends on the task to be accomplished andthe recover efficiency desired. The gas flowrate in flow channel 16 isbetween approximately 1 m/sec and 30 m/sec and amounts to preferablyapproximately 15 m/sec. Quick-return cam 38 has a forward-backward speedratio of approximately 2 to 3, the travel is approximately 2 cm, and thefrequency is approximately 2 Hz.

[0026]3 d) A fourth embodiment of the third additional means of theinvention, in which fibrous fabrics or pads having the propertiesdescribed above are used, is illustrated FIGS. 6a and 6 b. The containerconsists in this case of a tube 10 provided with an inlet 12 for thedust-laden gas and an outlet 14 for the cleaned gas, equipped withvalves 78. Inside tube 10, fibrous fabric 30 is inserted between twoconcentric tubes consisting of a grid of medium metal wire or thin metalrods. The tube formed by inner tubular grid 98 constitutes the flowchannel 16; it is attached to outer tubular grid 32 by a plate 52 with areinforced head. The cage can move up and down inside container 10,guided by two rods 100 which are firmly joined to grid 32 and whichslide in guides 102 mounted inside container 10, as shown in FIG. 6b. Afunnel-shaped conical plate 96 connects the lower end of outer tubulargrid 32 to the lower end of inner tubular grid 98. The cage, made oftubular grids 32 and 98, of fibrous fabric packing 30, reinforced-headplate 52, and cone 96, is shaken intermittently in a reciprocatingmovement by mechanism 50, which can be a quick-return mechanism or asimple cam mechanism. Drive shaft 36 is attached to reinforced plate 52by bellows 34 or by any other sealing element designed for the purpose.The dust falls into hopper 46 whence it can be removed through rotaryvalve 44. The diameter of inner tubular grid 98 is between 2 cm and 40cm, preferably between approximately 10 cm and 20 cm, and the thicknessof fibrous fabric packing 30 is between 2 cm and 15 cm, preferablybetween approximately 5 cm and 10 cm; the gas flowrate is betweenapproximately 2 m/sec and 30 m/sec. The length of tubular pad 30 isbetween 3 m and 30 m, depending on the task to be accomplished. In thecase of high gas flowrates, as are ordinarily encountered in industry, alarge number of inner tubular grids is attached to the samereinforced-head plate, and the array of tubes is fitted into a largeouter grid whose upper perimeter is attached to the plate with the head.The space between the inner tubular grids, the head plate, and the outergrid is packed with a fibrous fabric. At the bottom of the fibrousfabric, under each inner tube, is a funnel-shaped cone whose upper endis attached to the grooved bottom of the cage. The entire cage slidesinside a container and is shaken intermittently, in a reciprocatingmovement, by a shaker located at the upper end of the container. Thedust is sent to a hopper whence it is removed through a rotary valve.During tests performed with a layer 10 cm thick of a fiberglass pad witha porosity of 99.5% made of fibers with a diameter of approximately 30μm, the tubular gas flow channel 16 with an inside diameter of 20 cm, atube 3 m long, and a gas flowrate of between 12 m/sec and 18 m/sec, therecovery efficiency of standard ASP 200 test dust measured was 78%.

[0027]3 e) A fifth embodiment of the third additional means of theinvention, including fibrous fabrics or pads with the propertiesdescribed above, is illustrated by FIGS. 7a to 7 e. It has a rectangularcontainer 10 in which a rectangular cage 32 is placed, said cage beingfreely adjustable and being separated into four equal compartments byfluidtight partitions 90. The dust-laden gas penetrates through inlet 12into a tube comprised of an average-sized metal wire grid, first intocompartment 82, then into compartment 84, and then into compartment 86,and the cleaned gas finally leaves compartment 88 via outlet 14. Thespace between the cage and the tube comprised of a grid is packed with afibrous fabric. A flexible element 108, shown in the cross section ofFIG. 7c, connects inlet 12 and outlet 14 to the two ends of the tubewhose wall is composed of a grid. The outer appearance of the housing isshown in FIG. 7b, in which the positions of the sections are alsoindicated. The upper part of the cage is formed of a reinforced-headplate 52 connected by drive shaft 56 to a shaker which allows the cageto execute and alternately upward and downward movements. FIGS. 7d and 7e are two horizontal sections of the equipment whose positions areindicated in FIG. 7b. The dust shaken off the fibers lands in hopper 46from which it is removed by various appropriate means such as forexample a screw conveyor. The number of compartments or passages is notlimited to four as in this embodiment; they can also be numerous if thisis deemed necessary or appropriate. The dimensions chosen in thisembodiment are identical to those adopted in the previous embodimentillustrated in FIG. 6. This embodiment offers the possibility of using adevice with a flow channel whose useful length is the same as thatchosen for the previous embodiment, but whose height is very much less.

[0028]3 f) A sixth embodiment of the third additional means of theinvention, including fibrous fabrics or pads whose properties aredescribed above, is illustrated by FIGS. 8a and 8 b. It is comprised ofmodules formed of two fitted fibrous pads 30 approximately 1 cm to 2 cmthick, disposed horizontally or vertically, spaced 1 to 3 cm apart, andforming a channel 16 approximately 50 cm high and approximately 50 cmlong, through which the air/gas flow circulates in the form of aturbulent flow. According to a preferred form of this embodiment,represented by a top view in FIG. 8b, pads 30 are pleated, the pleatsbeing oriented perpendicularly relative to the direction of thecirculation of the turbulent gas/air flow, similarly to the screenswhose orientation is shown in FIG. 2. FIG. 8b also shows the holdingedges 24 disposed at the ends of each passage. Another feature of thisembodiment resides in the fact that the dust is collected on both sidesof the channel traversed by the turbulent gas/air flow. It is for thisreason that this embodiment is called a double-sided collector; thearrangement of the collecting pads 30 resembles that of the collectingelectrodes in plate-type electrical dust removers. In this embodiment,several modules (five in FIG. 8) such as those described and above anddisposed side by side are connected in series by U-shaped connectors 72such that the gas/air flow direction changes 180° each time the airpasses from one module to another. The dust-laden air-gas flowpenetrates through inlet 12 and the cleaned air/gas flow is exhaustedvia outlet 14. Fitted pads 30 are inserted into a structure 74 composedof two front plates and four partitions accommodated in housing 10 Thegas/air flow is introduced by means of fan 68 mounted on support 70.This embodiment is particularly advantageous for applications such ascleaning air in dwellings and offices where the air has little dust, sothat the fibrous pads do not require frequent cleaning. For unitsrequiring extremely high recovery efficiencies, pleated or flatcollector pads charged with static electricity can be used, and/or fordeodorization, pads containing an appropriate adsorbent such asactivated charcoal can be used instead of certain existing pads.Enlarged versions of the double-sided collectors of this embodiment canbe used for cleaning industrial gases. However, in this case, thecollector pads must be cleaned regularly by agitation or by anotherother appropriate method. In a test unit whose flow channel 16 is 1.3 cmwide and has a useful length of 2.5 m, pleated fibrous pads 30, 2.5 cmthick, and an air flowrate of 6.5 m/sec, the recovery efficiency ofstandard ASP 200 test dust measured was 92%. In the same test unit, withair moving at the same rate, 100% of the dust formed of particles 5 μmin diameter was collected from the ambient air in tests performed withpleated fibrous pads 30, 2.5 cm thick, and charged with staticelectricity.

[0029]3 g) The seventh embodiment of the third additional means of theinvention, including fibrous fabrics or pads, is illustrated by FIG. 9.It consists of a spiral configuration of pad 30 disposed on animpermeable sheet 106. This sheet, on which the pad is mounted, isspiral-wound such as to leave a space 16 between two consecutive turns,thus forming two parallel gas channels 16. The spiral turbulent flowdust remover is placed in a cylindrical container 10, with the inlet 12for the dust-laden gas being at its center and the outlet 14 for thecleaned gas being located tangentially on the outer periphery of thecylinder. The lid of the unit, to which the inlet is connected, is notshown in FIG. 9. As can be seen in this figure, this embodiment is alsovery well suited for cleaning air in dwellings and offices where the aircontains little dust. The unit requires only periodic cleaning atwidely-spaced intervals, which may be by agitation or by suction. Thewidth of an air passage is between approximately 1 cm and 3 cm. Thethickness of the pad is between approximately 2 cm and 5 cm and theheight of the unit varies between approximately 10 cm and 50 cm. One ofthe advantages of this spiral configuration resides in the fact that itfavors the appearance of turbulent flow conditions for Reynolds numbervalues (namely, for a given system, with a gas having a lower flowrate)that are lower than those encountered in a straight channel. Enlargedversion of the spiral turbulent flow dust remover can also be used forcleaning industrial gases. In this case, however, the collector padsrequire periodic cleaning by agitation or by any other appropriatemeans. In a test unit with a flow channel 16 with a width of 1.3 cm, afibrous pad 30 with a thickness of 2.5 cm, a useful length of channel 16of 3 m, and an air circulation rate of 2.5 m/sec, the recoveryefficiency of standard ASP 200 test dust measured was 92%.

[0030] In summary, the present invention provides a number of novelstructures and implementation methods for effective elimination ofparticles, generally of very small size, suspended in industrial gasesor in air. Modifications are possible without departing from theframework of this invention.

1) Device for eliminating the particles contained in a stream of fluidcomprising a container (10) with a passage for the fluid stream inturbulent flow and a plurality of objects oriented transversely relativeto the direction of flow, said objects having edges communicating withthe stream of fluid and defining between them at least one stagnantspace where the particles are recovered; characterized in that (a) theobjects are plates provided with slots that extend inward from saidedges; (b) or the objects are pleated elements such that each side ofthe pleats is in contact with the stream of fluid; (c) or the objectsare comprised of a fibrous pad, a fibrous mat, or a fibrous fabricdisposed along the gas stream; such that the slots, edges of the twosides of the pleated elements, or pads, fabrics, or fibers furnishadditional edges for catching particles. 2) Device according to claim 1,characterized in that said objects are also located near each other in adirection other than the direction of flow. 3) Device according to claim1, characterized in that said objects are charged with staticelectricity. 4) Device according to claim 1, characterized in that theturbulent flow is transformed into viscous flow in said spaces. 5)Device according to claim 1, characterized in that said objects areplates disposed near each other, transversely to the direction of flow.6) Device according to claim 1, characterized in that said objects arescreens with meshes located near each other, each being mounted on aframe, said mesh screens generally being placed transversely relative tothe direction of flow. 7) Device according to claim 1, characterized inthat the open channel is sloped such as to facilitate elimination of theparticles collected in said spaces by gravity. 8) Device according toclaim 1 having means for shaking and/or moving the surfaces on which theparticles are collected to facilitate their elimination. 9) Deviceaccording to claim 1, characterized in that the pad, the mat, or thefibrous fabric define the flow channel of the fluid stream. 10) Deviceaccording to claim 9, characterized in that said flow channel istubular. 11) Device according to claim 9, characterized in that saidflow channel has a pleated shape. 12) Device according to claim 9,characterized in that said flow channel has a spiral shape. 13) Methodfor elimination of particles contained in a fluid stream with turbulentflow, comprising penetration of vortices from at least part of saidstream into spaces defined between objects disposed near each other andrecovery of said particles from the surfaces of said objects as thevortices are damped.